Hydrophone with spaced electromechanical ceramic elements



United rates 3,627,540 Patented Mar. 27, 1962 Free Jersey "Filed Sept. 23, 1957, Ser. No. 685,644

2 Claims. (Cl. 340-) My invention relates to hydrophones. In particular, my invention relates to hydrophones which are entirely encapsulated and which may be produced economically and easily.

A principal object of my invention is to provide a hydrophone which is entirely encapsulated without the use of any seals.

A further object of my invention is to provide a hydrophone cable seal which is leakproof without the use of extra parts.

A still further object of my invention is to provide a hydrophone cable seal with a moisture barrier which prevents the cable seal from breathing.

Other objects and advantages of my invention will be apparent during the course of the following description.

By encapsulation, I mean filling the interior of the hydrophone and sealing it from the external water in which it is placed so as to make it and the elements contained therein waterproof.

In the accompanying drawings, forming a part of this application, and in which like numerals are employed to designate like parts throughout the same.

The single figure of the drawing illustrates one form of the hydrophone of this invention.

In the hydrophone illustrated in the drawing, electrical insulating tubular members 51 and 52 of Bakelite impregnated paper or similar material are set on an insulating cap 58 which is formed of Bakelite or similar material such that cap 58 fits snugly inside tube 51 and 52 is properly centered within tube 51. This centering may be accomplished by placing grooves in cap 58 (not shown) into which tube 52 is set. I prefer to form tube 52 with a plurality of openings 66 adjacent cap 58. Electromechanically sensitive bodies 53a, 53b and 530, which I prefer to form of piezoelectric ceramic such as the titanates, niobates or zirconates, are placed between tubes 51 and 52. Bodies 53a and 53b are held in spaced relationship by tape 63 which is attached to bodies 53a and 53b around their circumferences. In similar manner, bodies 53b and 53c are held in spaced relationship by tape 64. In place of tapes 63 and 64, insulating grommets may also be used. The spaces between bodies 53a and 53b and between bodies 53b and 530 are shown expanded in the figure for the purpose of clarity. Electrodes 54a, 54b and 54c are suitably aflixed to the outer surfaces of bodies 53a, 53b and 530, respectively, and electrodes 55a, 55b and 550 are similarly affixed to the inner surfaces of bodies 53a, 53b and 53c, respectively. The electrodes are applied to the surfaces of the ceramic bodies by any of the techniques which are well known in the art.

Bodies 53a and 530 are held spaced from tube 52 by grommets 56 and 57, respectively, which also serve to maintain the presence of the airspace between tube 52 and bodies 53a, 53b and 53c. Connections 61 and 62 are arranged so that the ceramic units are electrically connected in series and outside connections are made to the terminals of this series arrangement by leads 59 and 60. Lead is placed in the combination so that it extends for substantially the length of the hydrophone and is doubled back upon itself prior to being connected to electrode 540. As a result, it will be sealed within the potting for some length and cannot breathe at the point at which it enters the water. The scaling is accomplished by pouring potting 65, in its liquid state into the inner volume within tube 52. It fiows through openings 66 and fills the volume between tube 51 and the bodies 53a, 53b and 53c also. The potting is permitted to set and harden, at which time the combination, including the leads, is completely sealed. For potting 65, I prefer to use a potting compound consisting of an epoxy resin in combination with a hardening agent such as diethylene t-riarnine, and a plasticizer of a liquid polymer type such as has been described in the article Where and How to Use Epoxies by Jerome Formo and Luther Bolstad in Modern Plastics, volume 32, No. 11, pages 99 to 104. It can be seen that grommets 56 and 57 maintain the necessary airspace so that the ceramic elements may vibrate when subjected to excitation. Leads 59 and 60 may, if desired, be contained in a cable (not shown).

The operation of the hydrophone illustrated in FIG- URE 5 is standard in the art. It is hung in the liquid medium and suspended by its leads 59 and 60. Upon receiving acoustic waves at frequencies to which the unit is sensitive, the ceramic bodies 53a, 53b and 53c vibrate and generate an electric voltage which is transmitted by leads 59 and 60 to suitable amplifying and detecting equipment (not shown). The unit may also be used as a transmitter, in which case electrical excitation of the proper frequency is applied to the unit from a generator (not shown) through leads 59 and 60 thereby causing bodies 53a, 53b and 53a to vibrate and transmit an acoustic wave in the liquid medium.

While I have described my invention by means of a specific example and in a specific embodiment, I do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit of my invention or the scope of the subjoined claims.

Having thus described my invention, I claim:

1. A hydrophone comprising a pair of tubular insulating bodies, one within the other, a cap at one end of said tubular electrical insulating bodies such that said cap fits snugly within the larger of said pair of tubular insulating bodies, a plurality of cylindrical, electromechanically sensitive, ceramic bodies with electrodes afiixed to the inner and outer surfaces thereof between said pair of tubular insulating bodies, holding means, spacing means, said ceramic bodies being located one above the other and held in spaced relationship each from each by said holding means, said ceramic bodies being kept in spaced relationship with the smaller of said pair of tubular insulating bodies by said spacing means, said spacing means being placed at the extremities of said plurality of ceramic bodies, said ceramic bodies being connected in series, external electrical connections fed through said cap within said smaller tubular insulating body for a minimum distance substantially equal to the length of said smaller tubular insulating body and making electrical connections to the terminal electrodes of said series connected ceramic bodies, the space within said smaller tubular insulating body, below and above said plurality of ceramic bodies and between said plurality of ceramic bodies and said larger tubular insulating body being, filled with potting, said potting sealing said electrical connections at the points at which said connections leave the assembly.

2. A hydrophone as described in claim 1 wherein said smaller tubular insulating body contains openings therein adjacent the end adjacent said cap.

References Cited in the file of this patent UNITED STATES PATENTS 2,480,535 Alois et-ali Aug; 30, 1949 4" Frondel Oct. 25,1949 Gogolick et al July 29, 1952 Ianssen Nov. 18, 1952 Harris June 5, 1956 Harris Aug. 28, 1956 Vogel Sept. 4, 1956 Harnis Aug. 27, 1957 Harris June 3, 1958 Harris Aug. 19, 1958 Harris Mar. 31, 1959 

